The present invention relates to high-density ballast materials, which possess improved transparency within certain regions of the electromagnetic spectrum.
Some types of aircraft components require specifically shaped and placed high-density materials (ballast) to meet center-of-gravity and/or moment-of-inertia requirements. Conventional ballast materials comprise high-density metals. Tungsten is the most often used metal for ballast due to its very high density, availability and low cost. However, existing high-density ballast materials are incompatible with radar absorbing composite structures (RAS) because they are opaque in the RF spectrum causing RF energy to be reflected in stead of being absorbed: These existing materials severely limit the RF performance of components, which require ballast.
An approach for producing a material that is both highly dense and RF transparent is to encapsulate a high-density metal powder in a low dielectric resin. This results in a high-density dielectric compound (although less dense than pure metals). While this approach enables the incorporation of a ballast material into RAS designs, the resulting component electrical performance is limited due to the dependency of performance on the dielectric properties of the constitutive materials. Typically, the lower the dielectric properties, the better a RAS system performs. The encapsulated metal powder compounds (materials) are non-conductive, they tend to have relatively high dielectric properties, which limits the performance of the RAS system. Such metal powder-based composites are also extremely dependent on particle shape. The particles must be near spherical to achieve a low composite dielectric at high loadings. Production of near spherical powders is often difficult and tends to be very expensive.
The present invention has been developed in view of the foregoing, and to address other deficiencies of the prior art.
When an aircraft component has to act both as ballast and as radar absorbing structure (RAS), a unique set of material property requirements is required. To fulfill these dual requirements a material has to be both substantially transparent to radar and dense. The present invention provides a unique approach to meet these dual requirements which are normally mutually exclusive.
The present high density, low epsilon ballast materials allow for significant RF attenuation for aircraft components requiring ballast materials. This is made possible in accordance with the present invention through the use of a high-density compound that is RF transparent enough to be compatible with RAS.
An aspect of the invention is to provide a high density, low epsilon ballast material comprising dielectric ceramic particles in a polymeric matrix.
Another aspect of the invention is to provide a method of making a high density, low epsilon ballast material including the steps of mixing dielectric ceramic particles with a resin, and curing the resin to form a composite material comprising the dielectric ceramic particles in a matrix of the cured resin.
These and other aspects of the present invention will be more apparent from the following description.